A breakthrough research reveals the secret of Stonehenge: A solar calendar

And we know how it works.
Christopher McFadden

Stonehenge is one of the most famous ancient landmarks on the planet. Many theories abound about its purpose and origin, but one of the most popular is that it was some kind of gigantic stone calendar. 

Recent research published in the journal Antiquity from researchers at Bournemouth University appears to add further weight to this hypothesis by providing a suggestion as to how it may have been used. The work was prompted by recent new discoveries and modern analysis that led Professor Timothy Darvill to attempt to look at the site with fresh eyes. 

"The clear solstitial alignment of Stonehenge has prompted people to suggest that the site included some kind of calendar since the antiquarian William Stukeley," said Darvill. "Now, discoveries brought the issue into sharper focus and indicate the site was a calendar based on a tropical solar year of 365.25 days," he added.

One critical piece of evidence to support this appears to be the fact that the giant sarsen stones of the henge appear to have been added during the phase of construction that occurred around 2500BC. These stones are thought to have been sourced from the same area and subsequently remained in the same formation. If true, this would indicate that they worked as a single unit.

Based on this information, Darvell and his team analyzed the stones at the henge, paying particular attention to their numerology and comparing them with other known calenders of the period. By doing so, he was able to identify that they were most likely a solar calendar in their layout, suggesting they served as a physical representation of the year that helped the ancient inhabitants of Wiltshire keep track of the days, weeks, and months.

"The proposed calendar works in a very straightforward way. Each of the 30 stones in the sarsen circle represents a day within a month, itself divided into three weeks each of 10 days," explains Darvill. The distinctive stones in the circle, therefore, likely mark the start of each week.

Not only that but an intercalary month of five days and a leap day every four years were needed to match the solar year. "The intercalary month, probably dedicated to the deities of the site, is represented by the five trilithons in the center of the site," added Darvill.

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"The four Station Stones outside the Sarsen Circle provide markers to notch up until a leap day," he said. 

Based on this, the winter and summer solstices would be framed by the same pairs of stones every year. The other stones would have also played an important role, with one of the trilithons framing the winter solstice, indicating it may have been the new year. The layout of the stones would also act as a kind of "sense check" too to calibrate the calendar. Any errors in counting the days would be easily detectable as the sun would be in the wrong place on the solstices.

stonehenge ancient calendar
Source: Darvill et al

The ancient calendar is very strange to us today

The calendar, with its 10 days and extra months, is obviously a bit odd to us today, but, calendars like this were adopted by many cultures during this period. After all, our modern calendar is a relatively modern construction dating from the Roman period and modified by Pope Gregory XIII during the late-Middle Ages. 

"Such a solar calendar was developed in the eastern Mediterranean in the centuries after 3000 BC and was adopted in Egypt as the Civil Calendar around 2700 and was widely used at the start of the Old Kingdom about 2600 BC," explains Darvill.

This would raise the possibility that such ancient calendars, like Stonehenge, may have some much older cultural routes across Europe and the Middle East. This is supported by some other interesting archaeological finds nearby. For example, the nearby Amesbury archer, buried about the same period, was possibly born in the Alps and moved to Britain as a teenager.

Darvill now hopes that future research could shed light on these ideas. Further ancient DNA and archaeological artifacts could reveal even more connections between these disparate cultures. Whatever the case, the identification of a solar calendar at Stonehenge is important in and of itself and should transform how we see it.

"Finding a solar calendar represented in the architecture of Stonehenge opens up a whole new way of seeing the monument as a place for the living," Darvill said, "a place where the timing of ceremonies and festivals was connected to the very fabric of the universe and celestial movements in the heavens."

The study has not been peer-reviewed and was originally published on Antiquity


"Scholars have long seen in the monumental composition of Stonehenge evidence for prehistoric time-reckoning—a Neolithic calendar. Exactly how such a calendar functioned, however, remains unclear. Recent advances in understanding the phasing of Stonehenge highlight the unity of the sarsen settings. Here, the author argues that the numerology of these sarsen elements materializes a perpetual calendar based on a tropical solar year of 365.25 days. The indigenous development of such a calendar in north-western Europe is possible, but an Eastern Mediterranean origin is also considered. The adoption of a solar calendar was associated with the spread of solar cosmologies during the third millennium BC and was used to regularise festivals and ceremonies."